Pulping and bleaching of wood chips in a single stage with tertiary butyl hydroperoxide

ABSTRACT

METHOD FOR THE PULPING AND BLEACHING OF WOOD CHIPS IN A SINGLE STAGE USING TERTIARY BUTYL HYDROPEROXIDE IN AN AQUEOUS ALKALINE MEDIUM. THIS METHOD PREVENTS ATMOSPHERIC POLLUTION AS WELL AS WASTE WATER POLLUTION.

3,707,437 PULPING AND BLEACHING OF WOOD CHIPS IN A SINGLE STAGE WITH TERTIARY BUTYL HYDROPEROXIDE Robert M. Lincoln, Moylan, and Joseph A. Meyers III,

Springfield, Pa., assignors to Atlantic Richfield Company, Philadelphia, Pa.

No Drawing. Filed July 24, 1970, Ser. No. 58,198 The portion of the term of the patent subsequent to Feb. 29, 1989, has been disclaimed Int. Cl. D21c 9/16 US. Cl. 162-78 Claims ABSTRACT OF THE DISCLOSURE Method for the pulping and bleaching of Wood chips in a single stage using tertiary butyl hydroperoxide in an aqueous alkaline medium. This method prevents atmospheric pollution as well as waste water pollution.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a method for the single stage high-yield pulping and bleaching of wood chips using a combination of tertiary butyl hydroperoxide and an aqueous alkaline medium such as aqueous sodium hydroxide.

Prior art Wood pulps can be classified into four groups. Mechanical pulp or groundwood pulp is produced by a mechanical disintegration of the wood in the presence of water, generally by pressing the debarked logs against a grinding wheel rotated at high speeds. The yield of pulp is quite high generally from 90 to 95 percent. Chemi-mechanical pulps are obtained by a very mild chemical treatment to soften the wood without significant delignification. This treatment is followed by disintegrating mechanically to give a yield of pulp in the range of 80 to 95 percent. Semi-chemical pulps are produced by somewhat stronger cooking conditions wherein partial delignification occurs and this is followed by defibering with a mechanical treatment. Pulp yields are in the range of from 55 to 80 percent. Chemical pulps are obtained by a vigorous chemical treatment which removes interfiber lignins so that the fibers can separate without mechanical treatment or with only a minimum amount of mechanical treatment. The pulp thus produced in yields of about 42 to 58 percent requires strong bleaching since the chemical treatment frequently results in the production of a pulp which is considerably darker than the color of the original chips. Chemical pulps also contain high molecular weight lignin fractions which are not easily removed. Chemical pulping can be further sub-divided into alkaline pulping (the kraft process involving sodium hydroxide and sodium sulfide) and the acid pulping process. The chemical pulping methods produce high strength papers at a considerable sacrifice in pulp yield and in addition require extensive bleaching. In order to accomplish the bleaching, at least four separate stages are usually required. In the first stage chlorine is employed and thereafter the pulp is extracted with an alkaline solution. The next stage involves the use of hypochlorite and the final bleach is usually accomplished with chlorine dioxide. In certain instances one or more of these steps may be repeated.

United States Patent 0 Recently there has been proposed another chemical pulping method utilizing peractic acid in the first stage and sodium hydroxide in the second stage. This process is set forth in Canadian Patents 814,309 and 814,310. The pulp thus produced is unbleached and is generally darker than the original wood chips, thus it requires extensive bleaching with the same pollution problems found in the kraft process.

In United States Patent 3,428,520 there is shown a twostep process wherein an organic peroxy acidic compound is employed in a vapor phase cooking step at a pH of about 2.0. This is followed by an alkaline extraction step. This yields an unbleached semi-chemical type of pulp which requires extensive bleaching with the same pollution problems.

These prior art processes however, suffer from a common and increasingly serious problem namely that they seriously pollute the atmosphere surrounding such pulping plants and in addition the waste water from the plants pollutes both the ground water and streams with which it comes in contact. It has become increasingly obvious, not only to certain scientists and ecologists, but also to every segment of our population that pollution of all kinds must be controlled and eliminated. In the kratt process, although it is a so-called closed system it is in fact not a closed system. For example, in the burning of the lignin wastes rather large amounts of hydrogen sulfide, methyl mercaptan and dimethyl sulfide are released into the atmosphere. Not only are these compounds highly toxic but they are also among the most malodorous compounds known. Likewise in the bleaching step of the kraft process the waste Water contains chlorides and chlorinated compounds which are highly toxic and undesirable in streams or ground water. Moreover the compounds employed such as chlorine dioxide are highly toxic, explosive and require expert handling with highly specialized equipment.

In the sulfite processes (chemi-mechanical and semichemical methods) lignin sulfonic acids, sulfite and sulfur dioxide are the pollutants. The lignin sulfonic acids which pollute streams from these pulping plants are bio-hard i.e., they are not susceptible to bacterial degradation and the effects of sulfur dioxide in the atmosphere cannot be minimized.

In the method of the present invention, a high-yield pulp is obtained, the yield being comparable to that obtained by the semi-chemical pulping. The yield, however, is considerably superior to the yield obtained in the kraft process. The present method does not degrade the color during the pulping operation with the result the pulp obtained is not darker than the original wood chip and thus the extensive bleach which characterizes other prior art process and in particular the kraft process is avoided. Considerable delignification is obtained by the alkaline tertiary butyl hydroperoxide process of this invention while the cellulose is protected and color formation is avoided. The paper obtained from the pulp, therefore, is superior in strength to that obtained from groundwood or semi-chemical methods and is only slightly inferior to the strength of the paper obta ned from the kraft process.

The process of this invention, however has an even greater important advantage, namely it obviates completely the pollution problems associated with the prior art chemical processes which have been discussed and in addition does not present new or dangerous pollution problems. The tertiary butyl hydroperoxide is converted to tertiary butyl alcohol which when burned With the lignin is converted to water and carbon dioxide. It is so highly combustible that its combustion is complete and therefore does not product even small amounts of carbon monoxide. Alternatively, the tertiary butyl alcohol can be recovered as a valutable chemical compound.

The process of the instant invention also provides substantial amounts of bleaching with the result that the use of pollution type bleaches can be substantially eliminated. The sodium hydroxide employed in the process is recovered in the same manner as in the kraft process, i.e. during the burning of the lignin it is converted to sodium carbonate Which in turn is reacted with unslaked lime thereby regenerating the sodium hydroxide and producing the insoluble calcium carbonate a non-polluting chemical compound.

The advantages of the instant method of pulping over prior art methods, therefore, are the production of a high yield, semi-chemical pulp, by an alkaline pulping method, requiring little if any further bleaching. The yields are comparable to those of the groundwood and semi-chemical methods and superior to the kraft process. The process does not degrade the color of the pulp and the paper obtained from the pulp is superior in strength to the paper from groundwood or semi-chemical pulps while being only slightly inferior to kraft paper and finally, it is the only method known which can substantially completely eliminate environmental pollution.

SUMMARY OF THE INVENTION In accordance with this invention wood chips are digested with an aqueous solution of tertiary butyl hydroperoxide and sodium hydroxide. The hydroperoxide perferably ranges in an amount from 2 percent to 40 percent by weight based on the weight of the dry chips and the sodium hydroxide is in an amount such that the weight ratio of tertiary butyl hydroperoxide to sodium hydroxide ranges from 4:1 to 1:3 with from 2:1 to 1:2 being preferred.

The digestion can be carried out at a temperature in the range of from about C. to 150 C. and preferably in the range of from about 60 C. to 130 C., a particularly preferred range is from 80 C. to 110 C. At these temperatures digestion times of from 15 minutes for the higher temperatures to 120 minutes for the lower temperatures can be used. The digestion, however, can be carried out at ambient temperatures with greater efliciency with respect to chemical utilization although longer times are required. Thus reaction is time-temperature dependent i.e., with higher temperatures shorter reaction times can be used whereas with the lower temperatures longer reaction times are required. Satisfactory results are obtained with a ratio of total liquor to wood being in the range of from 1:1 to 3:1.

It is an object of this invention therefore, to provide a method for pulping wood chips in a single stage.

It is another object of this invention to provide a method for the alkaline pulping of wood chips in a single stage to produce a pulp having a color as good or superior to the color of the original chips.

It is another object of this invention to provide a method for the single stage alkaline pulping of wood chips to give a high-yield of pulp.

It is another object of this invention to provide a method for the pulping of wood chips which substantially completely avoids both atmospheric pollution and waste water pollution.

It is another object of this invention to provide a method for the single stage pulping of wood chips using an aqueous mixture of sodium hydroxide and tertiary butyl hydroperoxide.

Other objects of this invention will be apparent from the description f f rred embodiments an from the c ims.

4 DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of the instance invention is useful with both the wood chips derived from softwoods (those from some gymnosperms) and hardwoods (those from some angiosperms). From the softwoods the coniferous species such as cedar, fir, hemlock, pine and spruce are suitable. From the hardwoods the instant process is useful for pulping and bleaching such woods as alder, aspen, beech, birch, gum, oak and the like.

The instant process can be carried out either by batch procedures or continuously in accordance with well known paper mil engineering procedures. The liquor resulting from the treating step contains some unreacted tertiary butyl hydroperoxide together with tertiary butyl alcohol and the water soluble lignin derivatives. The tertiary butyl hydroperoxide and tertiary butyl alcohol can be recovered by distillation and the tertiary butyl hydroperoxide recycled to the process. Tertiary butyl alcohol can be sold as a chemical and the water solution of the lignin derivatives can be treated in accordance with well known methods to recover a large number of valuable compounds. In this respect the instant process is superior to the kraft process since in the latter process the lignin is in the form of sulfur derivatives and generally polymerization has occured so that it is almost impossible to recover byproducts and instead the lignin derivatives are simply burned. This, of course, leads to atmospheric pollution.

In recent years tertiary butyl hydroperoxide has become available in large commercial quantities, the most important method of production being by the oxidation of isobutane. This process produces an oxidate from which the tertiary butyl hydroperoxide can be obtained in pure form or the oxidate itself can be employed since it consists of a mixture of the hydroperoxide and tertiary butyl alcohol. The tertiary butyl hydroperoxide also has the advantage over organic peroxide compounds such as peracetic acid and the like in that it is stable and can be handled and shipped readily using normal precautions. Other organic peroxide compounds, on the other hand, are highly unstable and dangerous to ship since they are exceedingly unstable and explosive.

The sodium hydroxide utilized in the process can be ordinary commercial caustic and the process is carried out utilizing an aqueous solution of the tertiary butyl hydroperoxide and the caustic so that no difiicult handling problems are encountered and no special auxiliary solvents or specialized equipment need be employed.

The digestions of the wood chips in the aqueous solution of tertiary butyl hydroperoxide and sodium hydroxide can be carried out at temperatures in the rang of from about 0 C. to 150 C. A more preferable range is from about 60 C. to about 130 C., and in particular a range of from C. to C. is preferred. If it is desired to obtain the greatest possible efiiciency in chemical utilization, the digestion can be carried out at ambient temperatures. At this temperature, however, digestion times of several hours or days may be required, whereas at higher temperatures times of from about 15 minutes for the temperatures in the upper end of the range, to 2 hours or longer for temperatures in the lower end of the range can be used. The digestion is a time-temperature depending reaction. Atmospheric to reaction autogenous pressure can be used.

The concentration of the hydroperoxide can range from 2 percent to 40 percent by weight based on the weight of dry chips, although higher concentrations can be utilized. A range of from 10 to 35 weight percent based on the weight of the dry chips has been found to be completely satisfactory for most woods. The amount of sodium hydroxide employed is related to the amount of hydroperoxide used so that the weight ratio of tertiary butyl hydroperoxide to sodium hydroxide ranges from about 4:1 to, 1:3 with. a range of from about 2:1 to 1:2, being preferred.

The weight ratio of total liquor to dry wood preferably ranges from about 1:1 to 3:1, although higher or lower ratios may be employed with particular types of wood and digestion conditions.

These aforementioned conditions are generally applicable to the types of wood chips which have been mentioned, although it will be understood, of course, as is well known in the art that some types of wood are more easily pulped than others and accordingly the conditions can be varied from mild to severe to suit the particular type of wood being pulped and bleached.

In the examples which follow, the method of the instant invention is compared with the other processes for pulping and bleaching in order to provide a better understanding of the instant invention and its advantages in comparison with prior art processes.

The most important process is the kraft process since two-thirds of all wood pulp is manufacture by this process. Most of the ligning and hemi-celluloses are converted to the water soluble form by the digestion step, wherein an aqueous sodium hydroxide-sodium sulfide solution is used to cook the wood chips for several hours at 100 to 200 C. There is left the cellulose fraction (45-55 percent of the original wood) in the form of a highly colored pulp.

The principal advantage of the kraft process is the production of a very strong pulp while the lignin fraction is burned to supply power for the process. The disadvantages of the kraft process are the pollution problems from the digestion, burning and bleaching steps as has been described. Processes developed to avoid the disadvantages of the kraft process are those employing oxidants such as chlorite, hydrogen peroxide and peracetic acid. The advantage of these processes is higher pulp yields with less pollution, but these have not produced paper of sufiiciently high quality at an economic price. Accordingly, in

been sprayed, the chips were transferred to vessels of about 400 ml. capacity and because of the relatively low liquor to wood ratios there was usually no free liquor. The vessels were capped and kept in a controlled-temperature oil bath which had been preheated sufficiently above the selected temperature so that the heat flow to the vessels caused the temperature to fall to that for the reaction, which required about 3 minutes. To cook the times included the 3 minutes for the vessel to become heated to reaction temperature. At the end of the reaction time the vessels were withdrawn and quenched in cold water. Known amounts of water were added to facilitate removal of the product from the vessels. The chips and diluted spent liquor were left over night to equilibrate at ambient temperature and at about 12 percent consistency before withdrawing the liquor for pH determination. For yield and lignin determinations the cooked chips were collected and washed with several 12 hr. soakings in warm distilled water until the filtrate had a pH of 7-7.5 and was clear.

Klason ligning analysis were determined according to the method of The Institute of Paper Chemistry. Method number 428 which is essentially a modification of TAPPI Standard Method T 222 except that the precipitate was collected on glass fiber filters instead of crucibles.

In the examples which follow, the cooking and related data on the products obtained are set forth.

EXAMPLE 1 Several runs were made in accordance with the foregoing description in order to determine pulp yield and lignin remaining in the pulp, utilizing a reaction temperature of 100 C. but varying the other reaction conditions. The Klason lignin content of the original chips was 21 weight percent. The conditions and results obtained are set forth in Table 1.

TAB LE I Run number t-Butyl hydroperoxide, wt. percent I 18 18 15. 3 15. 3 0 0 l5. 3 15. 3 Sodium hydroxide, wt. percent l 0 0 8 16 8 16 16 16 Acetic acid, wt. percent I 4 0 U 0 0 0 0 Liqu'ornvood, wt. ratio 1. 2:1 1. 2:1 2:1 2. 4:1 2:1 2:1 2. 4:1 2. 4:1 Time in bath, min 60 60 60 60 60 60 30 15 Final pH 4. 3 5. 3 9. 6 12. 7 11. 6 13 12. 7 13 Pulp yield, wt. percent a 96 96 b 89 b 76 c 84 B 76 b 79 b 84 Klason lignin, wt. percent O.D. pulp. 21 21 18 14 21 21 15 18 Klason lignin removed, wt. percent 4 4 4 25 49 19 20 43 30 I Percentages on oven-dried wood basis unless noted otherwise. b Product at least as light in color as chips.

0 Product darkened to a tan color. Based on Klason lignin content of chips, 21 wt. percent.

the following examples, comparisons have been made with the kraft process, the peracetic acid process and the process of the instant invention.

The raw material for the examples which follow was prepared from the two peeled quaking aspen bolts which were chipped into about Ag in. chips in a 4-knife, 38-in. Carthage chipper. The chips were screened on a Sweco screen and the large knots and slivers were removed from the on-2-mesh fraction, the accepted chips were broken down further in a l2-in. Sprout-Waldron refiner fitted with B2975A spiked plates set at a near-zero gap. The chips, after this reduction, were put through a Sweco screen and the through-4on-10-mesh fraction were used in the pulping runs. These chips were about to in. cross section and approximately in. in length.

Solutions for treating the chips were prepared by mixing the required weights of aqueous solutions containing 10 wt. percent tertiary butyl hydroperoxide and 20 wt. percent sodium hydroxide, then, further diluting with water to the specified liquor to wood ratio.

The chips to be cooked were placed on a polyethylene sheet and turned over while being sprayed with a calculated amount of the appropriate solutions to achieve the diiferent liquor compositions used. After they had In order to understand the relationship between pulp yield and weight percent Klason lignin on dry pulp basis and the weight percent Klason lignin removed an explanation of these determinations is necessary. Thus, in run 4, for example, for each g. of chips, since the pulp yield was 76 percent, there would be 76 g. of pulp and 24 g. of the chips removed as solids in the liquor. Since the lignin content of the pulp was 14 percent, there would be 10.7 g. of lignin in the pulp and 10.4 g. of lignin in the solids of the liquor. Thus, in the pulp, 10.7 g. divided by 21 g. times 100 gives 51 percent of the original lignin and accordingly 49 percent of the original lignin had been removed. Runs 1 and 2, wherein no sodium hydroxide was employed, show that substantially no delignification is obtained. Runs 4 and 7 show high delignification, and in addition excellent color properties of the delignified pulp. Runs 5 and 6 show that in the absence of tertiary butyl hydroperoxide the pulp had very poor color and delignification was inferior.

EXAMPLE II Additional runs were carried out at higher temperatures than in Example I and under varying pH conditions, i.e. amounts of sodium hydroxide. Again the pulp yield and the amount of lignin remaining in the pulp was determined. Results of these experiments are set forth in Table II.

similar liquor to provide a basis for comparison with other pulps. Handsheet data are shown in Table for a normal TABLE II Run number Bath temperature, C 130 130 130 110 110 110 110 110 t-Butyl hydroperoxide, wt. percent 2O 20 20 20 20 20 20 Sodium hydroxide, wt. percent B 16 9 0 I6 16 16 9 9 Concentration H01, percent a 0 0 3.0 0 0 O 0 O L1quor:w0od,wt r 2:1 2:1 2:1 2:1 2:2 2:1 2:1 2:1 Time in b 15 30 60 60 90 Final pH 10.6 8.4 2. 7 12.0 11.6 11.3 8.6 8. 5 Pulp yield, wt. percent b 77 b 83 e 72 b 73 b 71 71 b 83 b 82 Klason iignin, wt. percent O.D. pulp"..- 13 16 ND 13 13 13 16 16 Klason iignin removed, wt. percent 53 36 ND 56 56 57 37 38 e Percentages on ovendried wood basis unless noted otherwise. b Chip-colored product.

6 Dark brown product.

d Based on Klason iignin content of chips, 21 wt. percent.

Nora-ND =Not determined.

These runs show that the pulp yield and lignin removal are not greatly effected by reaction time. They also show, however, that more lignin is removed when the ratio of sodium hydroxide to tertiary butyl hydroperoxide is relatively high. Run 11 shows that if no sodium hydroxide is employed, even under the most favorable conditions, and instead a low pH is utilized, the product obtained has a dark brown color. This product was obviously not in accordance with the objects of the invention. This result coroborates the results retained in Example I, runs 1 and 2, wherein no delignification occurred.

EXAMPLE III Another series of runs were carried out to show the influence of temperature and reduced amounts of tertiary butyl hydroperoxide at the higher pH ranges.

laboratory kraft aspen pulp and an unbleached high yield semi-chemical aspen pulp designated HYSC. This later pulp was obtained from an existing commercial mill. The material had been collected from the primary refiner in the system after 30 minutes at 175 F., with a yield of about 90 percent. Both of these pulps and also pulps S and HP were beaten in a Valley beater.

To prepare pulps S and HP for obtaining handsheet properties set forth in Table IV, the cooked chips plus liquor was put through a 36-in. style 185 Bauer double disc refiner. The Bauer machine was heated with live steam before using and continued during chip breakdown to a coarse pulp. The coarse pulps from the Bauer machine were diluted with water to about 5 percent consistency and fed through a 12-in. Sprout-Waldron laboratory refiner, and in a second pass the product was further diluted to 3 percent consistency and put through the same TABLE III Run number Bath temperature, C 100 100 100 t-Butyl hydroperoxide, wt. percent e 0 15. 3 I5 15 10 10 Sodium hydroxide, wt. percent 8 8 8 8 12 12 Liquor: wood 211 2:1 2:1 2:1 2. 4:1 2. 4.1 Time in bath, min- 60 60 60 60 30 60 in p 11.6 9.6 8. 7 7.9 12.4 12 2 Yield wt. percent b 84 89 86 d 85 83 d 79 Klason iignin, wt. percent 0 p 21 18 17 18 16 16 Klason iignin removed, wt. percent 19 25 30 27 37 40 Percentages on ovendried wood basis unless noted otherwise. 17 Brown-colored product.

0 Product as light colored as chips.

* Straw-colored product siightl darker than chips.

d Based on Klason content of chips, 21 wt. percent.

In order to consider the papermaking properties of the' pulps prepared in accordance with the instant invention, two pulps designated S and HP were prepared by cooking at the conditions shown in Table IV, then they were mechanically defibered as will be described. Pulp S was prepared with an alkaline liquor only, and pulp HP had machine. Each pulp was dewatered, and washed in a centrifuge.

All four pulps were beaten in the Valley beater in accordance with TAPPI Standard Method T 200 ts-66.

Handsheets for all the pulps were prepared according to TAPPI Standard Method T 205 m-58.

Sheet density, breaking length, burst factor, and Elmendorf tear factor were determined according to TA-PPI Standard Method T 220 m-60.

Tensile energy absorptions were measured according to TAPPI Standard Method T 494 su-64.

For breaking length and tensile energy absorption measurements a table model Instron tester was used. The initial jaw separation was 4.0 in., the test piece width L0 10 percent tertiary butyl hydroperoxide included in a 75 in., and the crosshead speed 1 in./min.

The results of the handsheet testing is shown in Table IV.

to obtain GE brightness according to TAPPI Standard Method T 217 rn-48 and 218 m-59.

TABLE IV Type of pulp HYSC S HP. Kraft Bath temperature, C 100 100 t-Butyl hydroperoxide, wt. percent.. 1 10 Sodium hydroxide, wt. percent 12 12 Liquorzwood, wt. ratio 2. 4:1 2. 4:1 Time in bath, min 35 35 12. 8 12. 4 90 85 81 Klason lignin, percent p lp 21 16 Klason lignin removed, wt. percent" 17 38 Handsheet properties:

Density, g./co 0. 55 00. 60 0. 55 O. 60 0.65 0. 55 0. 6t 0. 65 0. 70 O. 60 0. 65 0. 70 0. 75 Beating time, min 6 19 6 17 34 8 19 31 43 0 11 18 Breaking length, km 5. 5 6. 2 4. 2 5- 8 7. 4 4- 3 6- 1 7. 7 9. 0 5. 7 7.1 8. 4 9. 5 Tensile energy absorp, g.cm./cm. 40 44 39 52 24 38 55 75 29 50 70 91 Burst factor 26 3 20 26 3 18 28 37 45 21 32 42 52 Tear factor (Elmendori) 49 54 64 8 53 65 58 53 49 59 69 74 74 e Percentages on oven-dried wood basis unless noted otherwise.

The breaking length for pulp HP was found to be TABLE V very good and covering a much wider range than pulp HYSC and also a wider range than pulp S. The breaking length range of 4000-9000 In. for an 81 percent yield aspen pulp (pulp HP) is the same as that obtained with an 82 percent yield spruce pulp, described by Rydholm, Pulping Processes, p. 284, New York, Interscience 1965.

Tensile energy absorption properties of the handsheet from pulp HP are also very good. The tearing strength for the pulps shows that high values for pulp HP at relatively low sheet density as compared with the other pulps shown. These results show that high quality paper at least equal to or better than high yield serni-chemical pulp type papers and only slightly inferior to kraft type papers can be prepared by the method of the instant invention.

EXAMPLE V Two runs were carried out to compare cooking with tertiary butyl hydroperoxide and with peractic acid. As described in the prior art section herein, peracetic acid and alkali have been proposed for the pulping of hardwoods, including poplar, in 2-stages. To determine whether peractic acid and tertiary butyl hydroperoxide are interchangeable in such processing, runs were carried out modeled on the 2-stage process as set forth in Table V.

In carrying out these runs small chips were sprayed 0 with the appropriate amount of peracetic acid and cooked in accordance with the procedures described. To obtain pulps for making handsheets the cooked chips and liquor from two vessels (40 grams oven-dried chips per vessel) and the liquor were diluted with distilled water to 4 liters and then reduced to pulp by two passes through the Sprout-Waldron machine. The pulps were collected, washed, and deionized water, thickened, diluted to 10 liters with deionized water, and finally screened to provide a pulp for preparing the handsheets. It was observed that both types of the cooked chips required a high amount of mechanical energy to produce a pulp. The handsheets were prepared and tested according to the TAPPI methods noted above. The same pulps were used I, Reaction with oxidant:

Reagent Bath temperature, C 95 Amount of oxidant, wt. percent O.D. wood 8.8 8. 8 Liquorzwood 2. 2:1 2. 2: 1

Time in bath, min 60 60 Initial liquor pH 4.5 4.5

II. Reaction with alkali:

Bath temperature, C 95 95 Sodium hydroxide, wt. percent O.D. wood- 9.8 9. 8 Llquorzwood 7:1 7:1

Time in bath, min 60 60 Yield, percent. 85 77 III. Reduction to pulp: Screen r cts, wt percent pulp 35 11 IV. Pulp and handsheets properties:

Kappa number 92 Approx. Klason lignin, wt. percent O.D. pulp 21 14 GE bri htness 32 30 Sheet density, g./ec 0. 54 0. 50 Breaking length, m 4, 700 6, 3000 t-Butyl hydroperoxide.

Peracetie acid.

Calculated using the approximation Klason lignin=Kappa numberX0.15, as noted in TAPPI Standard Method T 236 m-60.

It will be seen from this comparison that tertiary butyl hydroperoxide does not delignify wood under these conditions since the pulp contains substantially the same amount of lignin as the original chips. The breaking length of the handsheets was poor and clearly, therefore, the tertiary butyl hydroperoxide is not the equivalent of peracetic acid. Finally, no bleaching occurs in the 2-stage treating process either with the tertiary butyl hydroperoxide or peracetic acid.

EXAMPLE VI Fifty grams of poplar chips, (nominal /3 inch) equal to 40.0 grams if oven dried, together with 20.0 g. t-butyl hydroperoxide, 8.0 g. sodium hydroxide and 224 g. of Water were slowly stirred in a round-bottomed flask for 3.5 hrs. at 85 C. The cooking solution and the chips were a light yellow color, the chips were soft and easily subdivided. After 20 seconds in a Waring Blendor with 300 ml. of water and pH adjustment to 6.4 by adding 8.0 ml. 10 percent sodium bisulfite, the pulp was filtered, water washed several times and oven-dried. The handsheet weighed 25.6 g. equal to 64 percent of the original chips. A Photovolt brightness on the dried handsheet was 86, for comparison a CEH kraft read 79 and a CEHD kraft read 91.

Analysis of the pulp for lignin gave an average value of 9.3 wt. percent Klason lignin; based on the 64 percent yield and a 19 percent lignin content for the original chips, two thirds of the original lignin had been removed.

A parallel experiment without tertiary butyl hydroperoxide, i.e. an aqueous sodium hydroxide digestion, gave a highly yellow-colored chip with little if any change in the chips physical structure, i.e. no fiber formation.

Based on the lignin removal, the appearance of the handsheet and microscopic examination, the product is classified as a bright semi-chemical pulp.

EXAMPLE VII EXAMPLE VIII Similar results were obtained with wood chips of other species including: loblolly pine, white spruce, tan oak,

black spruce, red maple, red oak. With each type of wood, bleaching and lignin removal were obtained.

EXAMPLE IX In order to show that ambient temperature treatments are effective, aspen chips g.) were allowed to stand at room temperature for one week with an aqueous solution containing 10 wt. percent tertiary butyl hydroperoxide, 4 wt. percent sodium hydroxide (50 g. solution per 10 g. oven dried chips).

The chips were separated, water washed and sodium bisulfite added to pH 6.5. After 1 hour in a Hobert mixer, the pulp was converted to a handsheet weighing 7.2 g. oven dried and having a Photovolt brightness of 76. For comparison, a CEH kraft read 79.

It will be seen from the foregoing description and the examples that the use of tertiary butyl hydroperoxide in the pulping of wood permits, for the first time, a practical method for alkaline pulping without excessive carbohydrate loss and without color formation. The method provides a practical means of obtaining color improvement over the original wood during the pulping operation, and also a practical means of obtaining a pulp which with a simple after-bleach gives a fully bleached commercial material. The product of the invention, as has been shown, is a bright semi-chemical pulp with strength and other physical properties only slightly inferior to kraft pulp. The process of the invention, however, has numerous advantages over the kraft process in that the instant process provides a high yield of pulp which does not have to employ the complex and expensive bleach required by kraft pulp.

Finally, the present pulping and bleaching process completely eliminates the pollution problems of sulfur pulping (the wraft or sulfite processes) as well as their chlorine bleaching pollution problems.

We claim:

1. A method for the pulping and bleaching of wood chips in a single stage which comprises treating said chips with a mixture consisting of tertiary butyl hydroperoxide and sodium hydroxide in an aqueous solution at a temperature in the range of from 0 C. to 150 C., at pressures ranging from atmospheric to the autogeneous pressure of the reaction at the temperature employed, the concentration of said hydroperoxide ranging from 2 to 40 weight percent based on the weight of the dry chips, the ratio of said hydroperoxide to sodium hydroxide ranging from about 4:1 to 1:3 and the weight ratio of total liquor to dry wood ranging from about 1:1 to 3:1.

2. The method according to claim 1 wherein the temperature is in the range of from C. to 130 C.

3. The method according to claim 1 wherein the temperature ranges between C. and C.

4. The method according to claim 1 wherein the hydroperoxide concentration is in the range of from 10 to 35 weight percent.

5. The method according to claim 4 wherein the weight ratio of the hydroperoxide to sodium hydroxide ranges from about 2:1 to 1:2.

References Cited UNITED STATES PATENTS 3,428,520 2/1969 Yiannos 162-38 3,514,278 5/1970 Brink 162-78 X 3,458,394 7/1969 Yiannos et al 8-111 X 1,767,543 6/1930 McKee et al 8-111 2,795,618 6/1957 Emerson et al 8-111 X 2,347,434 4/ 1944 Reichert et a1 162-78 3,645,840 2/1972 Lincoln et al. 162-78 OTHER REFERENCES Chemistry Of Organic Compounds, Noller, 1951,pp. 792-793.

S. LEON BASHORE, Primary Examiner A. L. CORBIN, Assistant Examiner U.S. Cl. X.R. 

